05000423/LER-1990-024

LER 90-024-00:on 900620,control Bldg Isolations Occurred Due to Radiation Monitor Detector Degradation.Other Equipment Not Affected.Degradation Caused Radiation Levels to Exceed High Alarm Setpoint.Detector replaced.W/900720 Ltr

ML20055H197
Person / Time
Site:	Millstone
Issue date:	07/20/1990
From:	Conway R, Scace S NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-024, LER-90-24, MP-90-727, NUDOCS 9007250303
Download: ML20055H197 (3)

LER-2090-024,

Event date:
Report date:
4232090024R00 - NRC Website

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.. . g Generd Offices Soloen Street, Berhn Connecticut NsfeTmasT[ed.'ttIYm1e r7co9mp *n7 P.O. BOX 270

@iD'as7Et7drIM*Nany HARTFORD, CoNNECTicVT 06414-0270 4 earmeast twear energy company ~

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July 20, 1990 MP-90-727 Re: 10CFR50.73(a)(2)(iv)  ;

U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555

Reference:

Facility Operating License No. NPF-49 Docket No. 50-423 Licensee Event Report 90-024-00 Gentlemen:

This letter forwards Licensee Event Report 90-024-00 required to be submitted within thirty (30) days pursuant to 10CFR50.73(a)(2)(iv), any event or condition that resulted in manual or automatic actuation of any Engineered Safety Feature (ESP).

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY

/ N k atq Stephen E. Scace Director, Millstone Station SES/RDC:ljs

Attachment:

LER 90-024-00 cc: T. T. Martin, Recion 1 Administrator ,

W. J. Raymond,' Senior Resident ins 3ector, Millstone Unit Nos.1, 2 and 3  !

D. H. Jaffe, NRC Project Manager, Millstone Unit No. 3 l

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NikO form abt, US NUCLE AR REGULATORY COMMISSION APPROVED OMB NO. 3160-0104

.- e (6-69) EXPIRE S: 4/3N92 Estimated turoen per respcese to comply with this entormation cohection roovest: 60.0 hrs Forwarc LICENSEE EVENT REPORT (LER) E$'ts'?*a'n"$,*In%,N**M0)'"* "s* u U':ieer keputatory Commission. Washingttw DC 20$$$ anc to tni, Paperwork Reouction proeect (3160 0104), Ottco of Management and buopet. Wasnin0 ton. DC 20603 DOWE1 NUMbEh G) " 'c F ACILIT Y NAME (1) hiillstone Nuclear Power Station Unit 3 o f s101010141213 1lOF 01 2 TITLL to)

Control Building Isolations Due to Radiation hionitor Detector Degradation EVENT DATE f6i LE A NUMPT A sei AFPOAT DATE th OTNF A F ACr.fTIE S INVOt vrD iti MONTF DAY NEAD YEAR @ MONTH DA- YEAR F ACILITY NAMEb 01 si ol of ol I I

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o 6.2l0 9' 0 9 l0 0l1l4 0l 0 0l ? 2l0 9l 0 olsiolofol l l OPfRATING THit REPOAT IS BEING BUDM!TTED PURSUANT TO THE REOUIREMENTS OF 10 CFA 6 (Check one or more et ine ionowing)(til 20 402(b) 20 402(c) 1 60.73la)(2)(iv) ] 73.71tD) 20 406teH1HU 60.36tc)(1) 60 73ta)(2)lv) 73 71tc) pow {'R - - ~

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At 1112 hours0.0129 days <br />0.309 hours <br />0.00184 weeks <br />4.23116e-4 months <br /> on June 20,1990, and at 1940 hours0.0225 days <br />0.539 hours <br />0.00321 weeks <br />7.3817e-4 months <br /> on July 1,1990, while operating in hiode 1,100% reactor power, $57 degrees Fahrenheit and 2250 psia, Control Building Isolation (CBI) signals were initiated by the A Train control buildirig inlet ventilation radiation monitor due to equipment degradation. On each occasion, the B Train monitor inclicated only normal br.ekground radiation. Control Room Operators blocked the Control Building pressurizauon and initiated irwestiitinm Cher equipment and systems were not affected. Actual radiation levels in the control room did not merease.

Root cause of the events was detector degradation which produced indicated radiation levels which exceeded the high radiation alarm setpoint and initiated the CBl signal.

The degraded A Train detector was replaced. The Preventive hiaintenance plan has been revised to include replacement of these detectors. All other detectors will be reviewed to determine if periodic replacement is needed by September 28, 1990.

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n TEXT CONTINUATION .no n. port, uanap.m.ni eranen in-c.30L U.S. Nucien' It eT*M0".E'dn $r'o*2I3SONMP'oSci o' Management and buopet. Washington 00 P0503 F ACILITY NAME o) DoOKET NUMDER (2) L F A NuupFm rp PAGE(3I YEAR E Millstone Nuclear Power Station Unit 3 ol 6l ol ol ol4 l2 l3 9l0 0l2l4 0l0 0l 2 OF 0l2 Text or mor. space e. reur.o. us .aoitionni Nec sorm a6sA si on

1. Dewnntinn of Event At 1112 hours0.0129 days <br />0.309 hours <br />0.00184 weeks <br />4.23116e-4 months <br /> on June 20,1990, and at 1940 hours0.0225 days <br />0.539 hours <br />0.00321 weeks <br />7.3817e-4 months <br /> on July 1,1990, while operating in Mode 1,100%

reactor power, 557 degrees Fahrenheit and 2250 psia, Control Building Isolation (CBl) signals were initiated by the A Tram control building inlet ventilation radiation monitor due to equipment failure. On each occasion, the B Train monitor indicated only normal background radiation. There is a 60 second time delay between initiation of a CBI signal and Control Building pressurization, which is designed to allow verification by operators. On both occasions, Control Room Operators blocked the CBI and imtiated investigations into causes of the events. Other equipment and systems were not affected. Actual radiation levels in the control room did not increase.

11. Cause of Event Root cause of the two events was detector degradation which produced indicated radiation levels which exceeded the high radiation alarm setpoint and initiated the CBI signals. Investigation of the June 20, 1990, event was unable to identify the root cause of the event, or reproduce the CD1 signal. {

Investigation of this event was still in progress when the July 1,1990, event occurred.

Ill. Annivtic of Event These events are reportable under 10CFR$0.73(a)(2)(iv), as events or conditions that resulted in manual or automatic actuations of an Engineered Safety Feature (ESF). Immediate notificat. ions were made in- I accordance with 10CFR50.72(b)(2)(ii). There were no sign!ficant safety considerations since actual high i radiation conditions did not exist. Each radiation monitor channel processes radiation counts from beta scintillation detectors, and provides indication and two alarms: one on radiation exceeding the high I radiation alert setpoint; and one on radiation exceeding the high radiation alarm setpoint. A CBI signal  ;

is initiated by either monitor when radiation levels exceed the high radiation alarm setpoint. Review of j computer logs for the June 20, 1990, and July 1,1990, events revealed that over a period of one to two minutes, indicated radiation increased above the alert setpoint, then exceeded the alarm setpoint thereby initiaung the CBI signal, and then decreased to less than the alert setpoint. Examination of the detector revealed that several components had deteriorated due to age. This detector had been installed for five s I

years. The B Train detector was replaced in May 1989 after being installed for four years, when it erroneously began to indicate increased radiation leveh above the high radiation alert setpoint.

IV. Corrective Action The degraded A Train detector was replaced. The Preventive Maintenance plan for the subject radiation monitors has been revised to include replacement of these detectors. A report on these events will be submitted to NPRDS. All other detectors will be reviewed to determine if periodic replacement is needed by September 26, 1990.

V. Additional Information g LER 66-11-00 reported spunous CBI signals generated by Electro-Magnetic Interference (EMI) in the A l Train and B Train radiation monitors. While this is classified an equipment failure, it is unrelated to the i detector degradation manifested through the events occurrmg on June 20,1990, and July 1,1990.

Software noise filters which prevent CBI signals due to EMI-induced radiation spikes are specifically designed to only filter out near-instantaneous events. Smce the June 20, 1990, and July 1,1990, events occurred over periods of one to two minutes, the software noise filter could not have prevented the CBI signals.

The (KDB Beta detector) radiation morutors discussed are model 450-860-L001, manufactured by Kaman Science Corp.

Ells Codes Systems Comnonents IL - Radiation Monitonnp System MON - Monitor gseformaee i